Norwalk school officials say security protocols at several schools have been lifted.
Norwalk High School and P-TECH Norwalk were initially placed in a hold at 11:45 a.m. in response to a police investigation of unidentified loud noises.
The hold was lifted as of 12:41 p.m.
Naramake Elementary School also lifted its secure protocol at that time.
Norwalk police say they concluded their investigation.
The noises most likely came from maintenance work happening inside Norwalk High School, according to school officials.
Nathan Hale Middle School also was placed under a secure protocol out of an abundance of caution while police investigated. That was lifted earlier Friday.
Officials say students and staff in all buildings are safe.